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Theses

Symmetry breaking of biofilaments

Abstract : The interpretation of micromanipulation experiments of biological macromolecules has only been possible thanks to the development of polymer science. Indeed, the theories developed in polymer physics are the tool of theorists to interpret the increasingly precise and complex experiments. Biological macromolecules are in general more complex than classical polymers with flexible chains, because their basic units, their "monomers" are very often macromolecules themselves. The most appropriate model for biopolymers is the worm-like chain model that imparts bending rigidity to biological filaments. Because of its simplicity and usefulness in interpreting micromanipulation experiments of single biological macromolecules, this model has become the basic model for any theoretical approach to the biophysics of biofilaments. The confotronic model of microtubules leads to the fundamental phenomenon of spontaneous symmetry breaking that explains how a microtubule, a hollow cylinder, can, under certain circumstances, form a micron-sized superhelix. This requires a general physical principle for the mechanism of spontaneous breaking of these biofilaments. In this thesis, we assume that biofilaments, being always immersed in a fluid medium, can experience surface stresses that create a mismatch between the elastic properties of the surface layer and the core. Such a mismatch leads a filament into a frustrated elastic state. The filament can reduce this frustration and minimize its elastic energy by adopting a bent conformation in a spontaneous symmetry breaking process induced by a new type of self-bending elastic instability.My work, presented in this thesis, has attempted to explore this new elastic instability in different biofilament models in both linear and nonlinear elasticity regimes. The basic elements of linear elasticity and the physics of individual chains or bundles are presented in Chapter 2. Chapter 3 is devoted to the general theory of buckling, the basic idea of this thesis being related to self-buckling. Chapter 4 presents the physical and biological properties of cytoskeleton biofilaments and some key experiments that support our theoretical work. In Chapter 5, I have tried to review the general notions of ground state and symmetry breaking in order to place them in the context of biophysics. This chapter also introduces the basic ideas behind confotronics theory. This chapter can provide a new and broader perspective on biofilament physics. The last three chapters, 6 to 8, present my work on elastic instability and spontaneous symmetry breaking induced by surface stresses. This area of research was completely unknown to me when I started this project, so I decided to write a story that tells all the topics I learned on the way to the results presented here. As a teacher, I tried to write a very educational thesis with all the necessary concepts introduced at the beginning of each chapter. I hope that in this way the thesis can be read by beginners in this field, as I was when I started.
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Submitted on : Wednesday, April 27, 2022 - 9:48:04 AM
Last modification on : Thursday, April 28, 2022 - 3:36:35 AM

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  • HAL Id : tel-03652794, version 1

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Tanguy Saïbi. Symmetry breaking of biofilaments. Physics [physics]. Université de Lorraine, 2021. English. ⟨NNT : 2021LORR0213⟩. ⟨tel-03652794⟩

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